Babble uses a "command" structure similar to that is found in IRC. You can add in basic Custom commands in the acp in the "custom commands" section of Manage. There will be another tutorial on how to add in advanced commands. Custom Commands are more or less simple text replacements.
When you go to the custom commands section in manage, you will be presented with a "stack", that has two options:
Command: here you enter the command that will trigger it. you can include the / or not, babble will know what to do. commands are case insensitive, so Test and test are the same thing, so avoid having commands that are only different in case. btw, commands that are found in babble by default are check for first, so any custom commands that have the same name as those, will more or less will be ignored.
Message: you enter the message you want to display when the command is issued. you can use html/bbc here as well (but the same limitations apply as it does for bots, you must white list any css classes/data controllers you wish to use in the editors settings). there are two special variables that you can use here, #users# will display the users name who used the command and #msg# (this is anything after the comman is issued, so if you have a /candy m&m's command, it will display m&m's for the msg portion of the command).
You can add or remove custom commands anytime you wish. you are also not limited by how many you can have, but it might be pricey if you choose to have thousands.
Custom Command filled out.